This invention relates to a method and apparatus for high-speed, non-impact, thermal printing which provides sufficient resolution to produce specific styles of fonts such as E13B, CMC-7, OCR-A, OCR-B, Farrington 7B and 12F, and 1403 and 1428 numeric, for example, and which provides also for printing on plain paper.
There appear to be three general print head configurations used in known thermal printers, and they shall be referred to herein as Types 1, 2, and 3 for ease of illustration.
Type 1 configurations have heating elements arranged in a horizontal line extending over the entire page width, allowing the printing of portions of multiple characters to occur simultaneously, with one dot line across the page being printed, line after line, from the top of the page to the bottom. This configuration is also referred to as a line printer.
Type 2 configurations have the heating elements arranged in a vertical line whose length generally does not exceed the height of a single character. Successive indexes in a horizontal direction are necessary to complete the characters. In other words, the print head is advanced horizontally to print one column of a character at a time.
Type 3 configurations have the heating elements arranged in a matrix (like a 5.times.7 matrix) to fill the entire matrix field. All the heating elements to be energized for a particular character are energized simultaneously. The matrix is then moved to the next character location to complete the printing of that entire character.
A limit on printing speeds with thermal printers is determined by the thermal response of the associated print head and the specific thermal paper used. Stated another way, the printing time is determined by the sum of the heating and cooling of the associated resistive or heating elements and the time required to move the associated print head or record medium to the next printing position. Generally, some smearing of the printing results when a heated print head is moved prior to being sufficiently cooled. A typical present-day printing time would require about 2 milliseconds for energizing the heating elements for the "burn" or heating, about 3 milliseconds for cooling the heating elements, and about 4 milliseconds for stepping the print head to the next printing location. Note that the cooling and stepping of the print head represent a serial operation. This serial operation limits the speed capabilities of the present-day, print heads, generally making them too slow for handling data output in high-speed, computer applications or systems, or other applications where high-speed printing is required.
Another problem is that many of the prior art thermal printers do not provide sufficient definition or resolution of the character printed when compared to laser-xerographic or ink-jet technologies.
Another problem with prior art thermal printers is that they generally employ specialized thermal paper which has a limited shelf life and is not the record medium of choice for a large number of applications.
Another problem is that certain printing styles or fonts using particular inks could be printed by only one or a few printing technologies. For example, the American Bankers Association utilizes a specific standard or font for printing account numbers, amounts, and the like on financial documents, like checks for example; the standard is referred to as the E13B font, and it is printed in magnetic ink of a certain type for use in character-recognition equipment. The prior art method of printing the E13B font generally is limited to using a formed character or type face and a magnetic-ink, impact ribbon to transfer the inked physical impression thereof to the record medium. Noise emission from these prior art impact printers is typically about 80 db A.